The present invention relates to a power-servo booster such as a brake booster, a clutch booster or the like. In particular, the invention relates to an improved reaction force mechanism of a power-servo booster.
As a reaction force mechanism in a power-servo booster of this kind, there has conventionally been known a type as shown in FIG. 1. Such a mechanism is described, for instance, in U.S. Pat. No. 3,110,031. In FIG. 1, reference numeral 1 denotes a push rod composed of a rod 2 and a fitting member 3 fastened to one end of the rod by brazing, welding or the like. The fitting member 3 is slidably fitted in a connection hole 5 which is bored in a power piston 4. Reference numeral 6 denotes a reaction disk positioned at the bottom of the connection hole 5. The reaction force which is transmitted from a master cylinder (not shown) to the push rod 1 is transmitted via this reaction disk 6 to a plunger 7. The force is then felt by a driver as a foot pedal force via an input shaft 8.
As a way of decreasing the fuel consumption of a vehicle, it has been required to reduce the size of the booster mounted on a vehicle as well as the weight thereof. In view of this requirement, various techniques have been proposed, for example, to reduce the thickness of the shell constituting the booster or the power piston or modify the construction thereof. However, in order to obtain a desired reaction force, in the reaction force mechanism of FIG. 1, the reaction disk 6 is provided at the bottom of the connection hole 5 and the fitting member 3 of the push rod 1 is positioned in contact with the reaction disk 6 so as to allow relative movement thereof with respect to the connection hole 5 through a predetermined distance. Therefore, the length of this connection hole 5 in the axial direction is the sum of the thicknesses of the fitting member 3 and the reaction disk 6. Thus, the length of the power piston in the axial direction must necessarily include some surplus length. Under these circumstances, it has been difficult to shorten the length in the axial direction.